Scientifically referenced blog about healthy eating

The Science of Stretching Before a Workout

When I walk into the box to warm up for my CrossFit workout, I do some various stretches, some squats, row 200 m, etc. I see other people doing a variety of things to warm up, as well. The general consensus about what kind of stretching is appropriate seems to change daily on exercise and health websites, so I dug into some science.

All scientists love review articles because they combine all of the currently accepted literature. The review article that I am going to discuss is this one by Phil Page, PT, PhD, ATC, CSCS, FACSM. “Current Concepts in MuscleStretching for Exercise and Rehabilitation.” (1)

The point of stretching is to increase range of motion (ROM). A lot of factors go into ROM. One is the shape and angles of your joints. Obviously, bone can’t be stretched out. Another factor is the geometry of the ligaments that attach muscles to bones. These also don’t really stretch. The only modifiable factor is muscle. Muscles provide two types to tension during a stretch: passive tension is caused by the physical condition of the muscle, the composition. This can be changed by exercise. Active tension by the muscle is the natural reflex reaction of the muscle to contract. Think of your fingers. You can bend them back quite far by force, but you can’t bend them back that far without the force. The muscles naturally contract. Stretching can increase the distance between the two areas that the muscle attaches.

There are three types of stretching: static, dynamic, and ballistic.

Static stretching, where you position a stretch and hold it, is the most common. Dynamic stretching is more active and mainly consists of doing the activity you are preparing for with exaggerated motions. For instance, when preparing for a run, warm up by running with knees higher than normal, or feet kicking back further than normal. Ballistic stretching is jerking on the muscle that you wish to stretch. An example: when stretching you hamstring, you kick your leg into the air. This can be dangerous to the muscles and is no longer recommended by health professionals.

There are two ways that static stretching can affect the muscles. One is actually physically lengthening the muscle. The other and more common is simply increasing the tolerance of the muscle to be stretched (2). Most studies have determined that 10-30 seconds is long enough for a static stretch hold, but others say 15 seconds is the minimum amount of time before any muscle lengthening occurs (3). Repeating static stretches 2-4 times can yield further improvements, but any more repetitions have no effect (4).

Has anyone ever done a surprise workout and not stretched beforehand? Didn’t that workout seem easier? It did for me. I thought maybe it was all in my head, but it turns out, I was right. Static stretching before a workout has been shown to decrease muscle strength, and decrease running and jumping abilities (5, 6). This phenomenon is not well understood and varies among individuals, but it has been termed: “stretch-induced strength loss” (7). Obviously, this condition does not last, but static stretching right before a workout could very well deter performance. One way to get around this is to practice “maximal contraction” before the static stretch. So flex the muscle you’re about to stretch as hard as you can, and then stretch it. This reduces the strength loss during static stretching. No one know exactly why this helps, but it has been hypothesized that the muscle undergoes something termed “autogenic inhibition” after contraction where the nervous reflex relaxes and allows the length of the muscle to increase (8).

While both static and dynamic stretching improve ROM equally (9), dynamic stretching done right before a workout can improve muscle strength and running and jumping ability during that workout (10, 11). Another benefit of dynamic stretching is the constant movement, which keeps muscles warmer and more active. It is also more specific in that you are warming up by doing the activity you are preparing for (12).

After all of this information, many people will still claim that they aren’t very worried about performance and statically stretch to prevent injury. Some studies claim that this is a valid point (13), while others say there is no significant of risk muscle injury by not statically stretching (14). Most experts agree that more evidence is required before it can be stated as fact that static stretching alone can reduce the risk of muscle injury (7, 14).

Both types of stretching are great for after a workout, but stick to the dynamic warm-ups before a workout to maximize performance. There are exceptions to this rule. Activities like dancing and gymnastics depend a lot more on flexibility than most other activities, and could be enhanced greatly by a static warm-up as well as a dynamic one (13). Better yet, do some yoga on your day off.

14. Small K, Mc Naughton L, Matthews M. A systematic review into the efficacy of static stretching as part of a warm-up for the prevention of exercise-related injury. Res Sports Med. 2008;16(3):213–231.